In industry and also in household environment materials that are alike or different to each other, e.g. metallic and/or non-metallic substrates, are joined together using adhesives or sealants. Various one-component and two-component adhesives are known. Both one-component (1K) and two-component (2K) adhesives are known that cure at room temperature (23° C.), so called 1K-RTV or 2K-RTV (Room Temperature Vulcanizing) adhesives. Adhesives that cure at higher or lower temperatures are also known. Two-component compositions comprise at least two-components; each component containing materials that react with materials in the other component to form a cured resin. Both components are generally able to flow so that they can be readily mixed.
There are several types of two-component adhesive systems known, e.g. systems based on polyurethane or epoxy resins or based on moisture cross-linking polymers. The present invention is related to the latter, namely moisture cross-linking polymers.
One of the components of two-component moisture cross-linking adhesive systems contains a substantially water free polymer or resin that cures with the aid of moisture (i.e. water) and optionally a cross-linking catalyst. The other component comprises moisture (for example in the form of water). Upon combination of the moisture cross-linking polymer and said moisture a cross-linking reaction takes place to form said adhesive. As the presence of moisture (e.g. water) would result in curing of the adhesive, an one-component adhesive comprising a moisture cross-linking adhesive is free of an effective amount of water (i.e. usually less than 0.5 w/w % (wt. %)). Curing takes place after application of the said 1K adhesive upon contact with the moisture of the air.
Both one- and two-component adhesive systems generally comprise rheology controllers, for 2K systems in either or both of the components. The adhesive or sealant must show different rheology characteristics at different times. At the time of application, good flow characteristics are required whereas directly after application high viscous behavior is required to achieve its high tack function. Thus the rheology characteristics of the adhesive composition need to be controlled in a very precise manner.
These rheology controllers increase the viscosity of the adhesive and thereby provide so-called early strength, meaning the strength directly after application of the adhesive and prior to the cross-linking and/or curing of the adhesive. Thus, rheology controllers are used to provide sufficient tackiness of the adhesive composition in the period directly following the application of the adhesive until the cross-linking has proceeded sufficiently. If, for example, the adhesive is used to fasten a plate on a vertical surface, the plate should be kept in position for the period of time it takes for the polymer to cross-link without falling down or sliding down.
A disadvantage of insufficient early strength is that the parts to be joined together have to be mechanically (or manually) fixed in position until the bond has developed sufficient strength, which is undesirable.
Another disadvantage of known one- and two-component adhesives is that the rheology controller increases the viscosity to such extent that application of the adhesive is impaired. For 2K adhesives, the rheology controller added to either or both of the components increases the viscosity to such an extent that the mixing of i) a relatively viscous component with a relatively liquid (less viscous) component or ii) two relatively viscous components is difficult. There is insufficient compatibility between the two components to achieve homogenous mixing in an easy way. A thorough mixing is required in order to get efficient and quick activation of the moisture cross-linking polymer. Specialized equipment is required for homogeneous mixing of the two-components, which is not advantageous.
It is therefore an aim of the present invention to provide both an one- and a two-component adhesive composition that solves one or more of the above problems of prior art adhesives.